1. Field of the Invention
This invention relates to the recovery of phenol values as cyclohexanol from a purification residue and more particularly to the recovery of phenol values as cyclohexanol from the purification residue obtained in the amine purification of phenol.
2. Description of the Prior Art
The production of cumene-phenol, i.e., phenol produced by the oxidation of cumene and the decomposition of the resulting hydroperoxide in the presence of an acidic catalyst, is well known in the art. While such phenol is satisfactory for many purposes, where it is desired to reduce this phenol to cyclohexanone, it is necessary to purify the phenol to remove impurities detrimental to reduction. Such a purification, which is herein termed "amine purification of phenol," may be performed by a variety of methods, all of which involve the addition to the phenol of an amine in order to remove carbonyl impurities from the phenol. Examples of amine purification may be found in U.S. Pat. No. 3,322,651 wherein nitrogen compounds such as ammonia, alkyl amine, dialkyl amine and aralkyl amine are employed; U.S. Pat. No. 3,692,845 wherein a polyamine such as hexamethylenediamine or hexamethylenetriamine are employed; and U.S. Pat. No. 3,187,050 wherein the trisodium salt of ethylenediaminetetraacetic acid and sodium hydroxide are employed to treat the phenol. In addition, the amine purification of phenol may be effected by a combination of the processes disclosed in the above patents, e.g. cumene-phenol may be treated with a mixture of hexamethylenediamine and the trisodium salt of ethylenediaminetetraacetic acid. Generally, after addition of the selected amine to the cumene-phenol, the mixture is distilled to produce phenol as distillate.
While these amine purification processes produce a relatively pure phenol as distillate, they have the disadvantage of producing as distillation bottoms a residue, herein referred to as the "purification residue," which contains from about 40 to 65 percent by weight phenol, in addition to impurities such as imines of acetone, acetophenone, acetol and mesityloxide together with alpha methylstyrene, methylbenzofuran, heavy metals, sodium phenate and other unknown impurities, in addition to unreacted treating agents. Since discarding this purification residue would effect a severe economic penalty, it is desirable to recover phenol values from the purification residue. While such a residue can be subjected to further distillation in order to effect removal of phenol, the phenol thus obtained contains an unacceptable amount of impurities carried over from the purification residue. The impurities present in the phenol thus obtained are heavy metals, including nickel, iron, copper, lead, zinc, cobalt, tin and chromium, silica, halogens, acetone, alpha methylstyrene, methylbenzofuran and unknowns. Of the foregoing impurities present in the phenol, acetone and halogens are known to inhibit hydrogenation reactions of phenol. In addition, impurities such as iron, copper, zinc, and tin present in the phenol are known to poison hydrogenation catalysts and thereby necessitate frequent regeneration of the catalysts. Thus, phenol distilled from the purification residue is not suitable, for example, for hydrogenation to cyclohexanone.